438 IIOFMEISTER, ON 



fact that the first axis of their embryo has only a very 

 limited longitudinal development ; it is an axis of the second 

 order which breaks through the prothallium and becomes 

 the principal axis ; and they all agree further in this, that 

 the end of the axis of the first order never forms the root. 

 All vascular cryptogams are without main roots ; they have 

 only adventitious ones. 



In more than one respect the formation of the embryo of 

 the Coniferae is intermediate between the higher crypto- 

 gams and the phaeuogarns. Like the primary mother-cell 

 of the spores of the Rhizocarpeae and Selaginellae the 

 embryo-sac is one of the axile cells of the shoot, which in 

 the one case becomes converted into the sporangium, in 

 the other into the ovule. In the Coniferae also the embryo- 

 sac soon becomes free from any mechanical connexion with 

 the surrounding cellular tissue. The filling of the embryo- 

 sac by the endosperm may be compared with the produc- 

 tion of the prothallium of the Rhizocarpeae and Selaginellae. 

 The structure of the corpuscula bears the most striking 

 resemblance to that of the archegonia of the Salviniae, and 

 still more of the Selaginellse. Irrespective of the different 

 mode of impregnation — which in the Rhizocarpeae and 

 Selaginellae takes place by free spermatozoa, and in the 

 Coniferae by a pollen-tube, in the interior of which sperma- 

 tozoa are probably formed — the transformation of the 

 germinal vesicle into the primary mother-cell of the new 

 plant in the Coniferae and the vascular cryptogams, only 

 differs in the fact, that in the latter there is usually one 

 single germinal vesicle only, whilst in the former there are 

 very numerous germinal vesicles, of which, normally, one 

 only is impregnated. The embryo-sac of the Coniferae 

 may be looked upon as a spore remaining enclosed in its 

 sporangium ; the prothallium which it forms does not come 

 to the light. In order to reach the archegonia of this 

 prothallium the impregnative matter must make itself a 

 passage through the tissue of the sporangium. 



Moreover, the development of the pollen of the Coniferae, 

 when dispersed, varies in a marked manner from that of 

 phaenogams, and exhibits vital phenomena similar to those 

 met with in the microspores of Pilularia, Salvinia, and 



